Elements for regenerative heat exchangers

ABSTRACT

A corrugated plate for use in the regenerative mass of a rotary regenerative heat exchanger has also alternating, approximately square-shaped, flat-topped protuberances between the corrugations so that the gas passage formed between it and an adjacent plate of the pack and defined laterally by the corrugations is alternately and regularly constricted and expanded.

United States Patent [72] Inventor Gerhard Kritzler Freudenberg, Germany [21 Appl. No. 854,854

[22] Filed Sept. 3, 1969 [45] Patented Jan. 12, 1971 [73] Assignee Apparatebau Rothemuhle Brandt &

Kritzler Westphalia, Germany a company of Germany [32] Priority Sept. 7, 1968 I 33] Germany [54] ELEMENTS FOR REGENERATIVE HEAT EXCHANGERS 6 Claims, 1 Drawing Fig.

[52] US. Cl 165/10, 165/ 166 [51] Int. Cl. F28d 19/00 WWI/l wyygew [50] Field of Search 165/ 10, 151, I66

[56] References Cited UNITED STATES PATENTS 2,696,976 12/1954 Boestad et al. 165/10 2,940,736 6/1960 Odman 165/166 3,151,675 10/1964 Lysholm 165/166 Primary Examiner-Albert W. Davis, Jr. AttorneyLackenbach & Lackenbach ABSTRACT: A corrugated plate for use in the regenerative mass of a rotary regenerative heat exchanger has also alternating, approximately square-shaped, flat-topped protuberances between the corrugations so that the gas passage formed between it and an adjacent plate of the pack and defined laterally by the corrugations is alternately and regularly constricted and expanded.

I I I I PATENTEU JAN 12 I971 I 8; 554,273

--- #if a Ill INVENTOR GERHARD KRITZLER BWW ATTORNEYS BACKGROUND OF THE INVENTION and of forming narrow channels parallel to the axial direction of the regenerator, through which the heat-exchanging media periodicallypass, alternating in counterflow, whilst the protuberances between the corrugations-in the walls of thenarrow gas passage ducts which are formed between the adjoining metal plates, are intended to create morefavorable flow conditions for the heat exchange.

It is known in the artthat IfOl' fulfillment of these requirements the metal platesmustbepacked as densely as possible, so that the gas passage ducts, which are formed between the alternatingly adjoining metal plates have the smallestpossible hydraulic radii, which are-normally chosen of a size ranging between 3to mm, in the range of gasvelocities of 5-15 meters/second, which areusually used, such small hydraulic radii create a laminarflow, with a heat transfer which is substantiallylowerthan thatof-aturbulent flow. The shaping of the gas passage ducts and: consequently the design of the protuberances in the plates themselves has therefore-a chief aim of influencingthe flow in such a way that this results in heat transfer coeff cients which will bev approximately the same as those ofturbulent tlow. r

Forthis purpose it has already been attempted to increase the extent of the heat transfer between the flowing gases and the metal plates by designingthe walls of the narrow gas passage ducts irregularlyandintermittently, wherebyan increased vortex shedding'within the flow. is obtained.

Experience has shown, however, that stronger and irregular vortexsheddings of this ,type cannot increase the heat transfer proportionallyto the increased loss in pressureduring passage ofthe flow. through a pack of such'm'etal heating elements.

One example of 1 what has, therefore, been normal practice to usein metal heating element-packsfor regenerative heat lic radius of approximately 3.5 mm.

SUMMARY OF THE INVENTION The present'invention has the object of improving the heat transfer in the narrow flow ducts between the metal heating elements, with the packing density remaining unchanged, by creation of periodically repeated delays and accelerations of the flow, which areco'nnected withan increased turbulence.

According to the present, invention this object is fulfilled in that the spacing metal heating element'shape between the planar 0r shallowly undulated plates is provided at specified distances with deep corrugations, which run parallel to the direction of flow of media through the pack and delimit the small gas passage ducts between the metal plates, which form with a specified hydraulic radius sihalL'rectangular flow cross sections for the gases, the'broader delimitation walls of which have at intervals in the flow direction laminar protuberances,

mainly of a square shape, which-are alternately arranged and directed opposite to each other in such away, that they constrict theflow cross, sections at one position into a small gap protuberance height, and this protuberance height amounting to approximately 50 percent of the distance of the plates from each other.

For further development of the invention the distance apart of the deep corrugations shall amount to 10-20 times the size of the hydraulic radius of the small flow passages between the metal plates, whilst the length along the direction of tlow of the laminar protuberances between these corrugations shall amount to 10-15 times the size of this hydraulic radius.

DESCRIPTION OF A PARTICULAR EMBODIMENT One part of an example of the invention is shown schematically in the drawing, which is a perspective, partly cutaway view.

It shows part of a metal element 1 with one wave of anapproximately sinusoidal corrugation each of an amplitudec/Z 1.0 to 1.2 r,,, of a wave length of l to 6.3 r,, and parallel to each other at distances of a 10-20 r where r, is the hydraulic radius of gas passage ducts which are formed by the corrugations. The plates 1 are made up into packs with shallowly undulated plates '2 or plane plates 2a alternately with the plates 1. The packs are placed in a regenerator chamber so that the corrugations are along the axial direction, and gas flow takes place in the directions of the arrows F1 and F2. Thecorrugations, parallel to the flow direction, space apart the plates 2. or hand the corrugated metal plates 1, so that the gas passage ducts are formed between them. The plates are placed alternately on each other. Only a portion of a whole pack is shown in the FIG.

Between the corrugations, therefore, there are generally rectangular section gas passage ducts. The major walls of 1 these have, however, generally square-shaped flatridges and furrows which are protuberances 3 pressed alternately from opposite sides into the spacing elements 1 at distances b 10- 151,, and having in each case a transverse width of 0.8- 1.0 b.

In the perspective illustration of the metal heating element 1 a cutaway portion of one of the metal plates 2 with shallow undulations has been shown on the top left-hand comer and also a next succeeding spacing element la. The undulations of these metal plates 2 which are alternately arranged between the-metalplates l have an amplitude height of 0.4 n, and an undulation length (wavelength) of approximately'5 r,,.

Compared with these rather weakly undulated intermediate plates Zthe ridges of the luminar, approximately square protuberances 3 of the wider wall parts form within the gasflow ducts between the heating elements-1 and 2 alternately quite considerable cross-sectional constrictions and correspondingly big expansions, because their protuberance depth-h amounts to approximately 0.3 to 0.7 r,,.

By means of a metal heating element pack,.whichis formed in c this way with alternately assembled plane or eundulated metal. plates 2 or 2a and themetal heating velements11;..with deep spacing corrugations, running parallel ,to the flow direction, periodically repeated delays .and accelerationsv of the flow are obtained within the flow ducts. between. the metal plates because of the considerable crossrsectional. constrictions and the cross-sectionalexpansion being alternatelyprovided thereto, which are due to the approximately la fand a p'roturberance depth h, said delays and accelerations increasing theturbulence'to such an extent that compared 1 to.= the previously conventional metal heating element pack,- for-.example according to the German Utility Model 1-,903,543,with parallel ducts and triangular flow cross sections, aconsiderable increase of the heat transfer coefficient is obtained in line with a simultaneous lowering of the pressure losses.

The proportional increase of the heat transfer FIGS.

amounts in the velocity range of the gas flow from "El- 6 meters/second to approximately 20 percent whilst the 1 pressure losses, compared to those of the previously used metal heating element packs, are about 40 percent lower, if flow-velocities of up to 6 meters per second are concerned.

and at anotherinto a larger-gap, the gapsdiffering by an equal I claim:

1. In a regenerative heat exchanger element pack formed of alternately assembled metal plates and spacing plates, which spacing plates are provided at intervals with deep corrugations, running parallel to the flow direction of gases through the pack and delimiting gas passage ducts between the plates, the improvement comprising in the flow cross sections of these small gas passage ducts having a small hydraulic radius r,, and a generally rectangular cross section with major and minor walls, the major delimitation walls of which having at equal distances behind each other in the flow direction flat protuberances of a generally square shape and of a height h, which are alternately arranged and directed opposite to each other in such a way, that they alternately constrict the flow cross section of the gas passage ducts, whereby this protuberance height h amounts to 0.30.7 r,,.

2. The improvement according to claim 1, being thereby characterized that one approximately sinusoidal corrugation each of an amplitude height of /2 1.0-1.2 r,, is provided at parallel distances of a -20 r, in the spacing plates and parallel to flow direction.

3. The improvement according to claim 2 being thereby characterized, that the approximately sinusoidal corrugation has an undulation length of l to 6.3 r,,

4. The improvement according to claim 1 being thereby characterized that the approximately square protuberances are indented behind each other in flow direction at distances of b l0- l 5 r with an area size of approximately I)".

5. In a regenerative heat exchanger element pack, a metal spacing plate having a mean plane, parallel spaced-apart corrugations passing through that plane, and, between the conugations, protuberances projecting out of the mean plane, adjacent protuberances in directions parallel to the corrugations projecting out of the said plane in opposite directions to an equal height, the said adjacent protuberances being llat surfaced and having a length equal to their width in a direction perpendicular to the direction of the corrugations.

6. A metal spacing plate according to claim 5 wherein the said adjacent protuberances are spaced apart, in a direction parallel to the corrugations, by a distance approximately equal to their length. 

1. In a regenerative heat exchanger element pack formed of alternately assembled metal plates and spacing plates, which spacing plates are provided at intervals with deep corrugations, running parallel to the flow direction of gases through the pack and delimiting gas passage ducts between the plates, the improvement comprising in the flow cross sections of these small gas passage ducts having a small hydraulic radius rh and a generally rectangular cross section with major and minor walls, the major delimitation walls of which having at equal distances behind each other in the flow direction flat protuberances of a generally square shape and of a height h, which are alternately arranged and directed opposite to each other in such a way, that they alternately constrict the flow cross section of the gas passage ducts, whereby this protuberance height h amounts to 0.30.7 rh.
 2. The improvement according to claim 1, being thereby characterized that one approximately sinusoidal corrugation each of an amplitude height of c/2 1.0- 1.2 rh is provided at parallel distances of a 10- 20 rh in the spacing plates and parallel to flow direction.
 3. The improvement according to claim 2 being thereby characterized, that the approximately sinusoidal corrugation has an undulation length of 1 to 6.3 rh
 4. The improvement according to claim 1 being thereby characterized that the approximately square protuberances are indented behind each other in flow direction at distances of b 10- 15 rh, with an area size of approximately b2.
 5. In a regenerative heat exchanger element pack, a metal spacing plate having a mean plane, parallel spaced-apart corrugations passing through that plane, and, between the corrugations, protuberances projecting out of the mean plane, adjacent protuberances in directions parallel to the corrugations projecting out of the said plane in opposite directions to an equal height, the said adjacent protuberances being flat surfaced and having a length equal to their width in a direction perpendicular to the direction of the corrugations.
 6. A metal spacing plate according to claim 5 wherein the said adjacent protuberances are spaced apart, in a direction parallel to the corrugations, by a distance approximately equal to their length. 